Plenty of acceptable options below. I would hesitate to suggest anything without knowing the usage of the function better. I like Guillaume's answer, but I tend to be fussy about function signatures and like parameters and arguments to be intuitively named so would probably ask the calling function to pass in either 'length' or 'step' rather than 'opt1' or 'opt2'.
But then again that depends on what the calling function 'knows'. It may be that the best solution is for the calling function itself to create the vector v by its chosen method and just pass it in as one single unequivocal argument.
The problem of defining a regular grid, which looks similar to what you are doing, always causes me problems though when I want to define a start and then either a size and an end, a step and an end or a step and a size to parameterise the grid!
